1. Field of the Invention
The present invention relates to an amplifier device with a number of amplifiers and a number of outputs.
2. Description of the Prior Art
Amplifiers of the above type are generally known. They are used, for example, in radio-frequency transmit devices (e.g. radar antennas or magnetic resonance antennas).
Radio-frequency transmit devices often include a number of transmit antennas which interact with each other. Each transmit antenna is fed with a transmit signal with the correspondingly transmitted signals being overlaid with the transmit signal—depending on the area of application—in the near field or in the far field. With magnetic resonance antennas for example the spatial distribution of the so-called B1 radio-frequency field can be adjusted by means of the overlaying of the individual signals that are emitted. With radar systems the directional characteristic of the emitted signals can be influenced by means of the overlaying of the emitted signals.
The generation of a suitable small signal (subsequently called an input signal) for each individual transmit antenna, supply of each input signal to an amplifier and feeding of the amplified input signals to the transmit antenna as transmit signals is known. The procedure has a number of disadvantages. Thus, for example, the transmit antennas are not decoupled from each other. Thus strong feedback at the amplifiers generally occurs which the amplifiers must overcome.
Operation of the antennas in Eigen modes is also known. In this case mode signals are created which are characteristic of the strength with which the transmit antennas in their entirety are to be operated in the relevant mode.
The modes are—at least in theory—orthogonal to each other, so that no feedback occurs. Even in practice often only slight feedback occurs.
The power consumption of the individual modes as a rule varies greatly from mode to mode. If equal size amplifiers are used to amplify the mode signals, all amplifiers must be dimensioned for the maximum power, so that the amplifier device overall is over-dimensioned and consequently expensive. If amplifiers of different powers are used, the amplifier device has a greater type diversity of amplifiers, which in particular makes keeping spare parts and repair more expensive.